This invention relates to a switched direct voltage converter comprising a control circuit and at least one semiconductor switch controlled by the control circuit via a switching input. The semiconductor switch is formed with at least one pair of series-connected complementary field effect transistors having through-connected voltage-controlled gate electrodes. The direct voltage converter is provided with an input terminal for connection to a direct voltage supply source and an output terminal for the supply of a converted direct voltage obtained across a capacitor by switching the semiconductor switch between supply voltage terminals via the switching input.
A direct voltage converter of this type is described n U.S. Pat. No. 4,302,804. The input terminal conveying the direct voltage is connected via a series arrangement of diodes to the output terminal which is coupled to ground via the said capacitor. Except for the diode connected to the output terminal, each diode has an electrode coupled to ground via an associated semiconductor switch. A series junction point between the pair of complementary field effect transistors is coupled via an associated capacitor to the other electrode of the diode. The switching inputs of the semiconductor switches are connected in the control circuit to outputs of a counting circuit to which clock pulses are applied. Under the control of the clock pulses the semiconductor switches are alternately switched in a cycle between the input direct voltage and the ground potential so that, dependent on the number of diodes and capacitors, a voltage multiplication is obtained because the capacitor voltages are added together in series and together supply the converted direct voltage across the first-mentioned capacitor.
Dependent on the number of capacitors and diodes in series, output voltages are obtained of the order of 1, 2, 4, 8 times etc. the differential voltage of the input voltage and a diode voltage drop. Intermediate values cannot be generated without taking further measures. The use of a large number of diodes and associated capacitors suitable for conveying the multiplied voltages is noted as a further drawback. There is also a voltage drop across each of the conducting diodes, which drop is substantially independent of the current derived from the output terminal by a load connected thereto. The result is a dissipation which is larger than in the case where the voltage drop is dependent on the current.